My masthead was struck a few years ago (see picture of melted VHF whip) and my limited experience (and extensive reading) tells me that you can't predict lightning. (Stainless melts at around 4,000 degrees F.)

Assuming your mast is aluminum (not CF) I think you should skip the air terminal. Here's why:

1) You already have a low-impedance path down the mast. If it gets struck the lightning charge will take the path of least resistance BUT it will also flash elsewhere at random, including everything with a wire on it, and there's nothing you can do to stop your VHF "system" from being fried. Lightning is "screwy" -- note that it unscrewed or blew off the PL-259 connector on my antenna (which went missing) and blew up the Windex (found fragments on the deck) but the Raymarine wind indicator sensor was untouched and still functioned. The tri-color still worked afterword, but the deck/steaming light and loudspeaker mounted at mid-mast did not. Most of the Raymarine electronics didn't work, the FM/CD stereo fried, and the engine control harness diodes were fried (which meant I couldn't start the engine).
2) It WILL interfere with the radiation pattern of your VHF whip. You will not have full omni-directional capability anymore. The ground plane in parallel with the whip will result in a signal radiation pattern skew that will reduce performance, at least in some directions.

3) It's extra weight aloft.

All that said, do it if you think it will make you feel safer. Your opinion is more important than mine.

PS - I don't buy into the brush type terminals either. I'm of the school that believes you should have a low-resistance direct path from top of mast to ground, and for human safety I want the top of the mast to be struck with the main bolt, not somewhere lower. (My mast was/is grounded to a Dynaplate below water. That was installed at the factory at request of the original owner.) Whether you have a blunt top (with corners) or a pointed top probably won't matter.